ABSTRACT The application aims to identify potential roles and molecular mechanisms of netrin-1 and netrin-1 pre-conditioned endothelial progenitor cells (EPCs) in vascular protection, specifically related to their anti-restenosis and anti- atherosclerosis effects. Four entirely novel hypotheses will be addressed: 1) Netrin-1 pre-conditioning protects EPCs from oxidative stress induced apoptosis through PI3K-dependent p70s6 kinase activation and Bim inhibition; In addition, mechanistic pathways mediating novel regulatory miRNAs-dependent enhancement of EPC survival by netrin-1 will be fully delineated. By targeting these novel mechanisms, EPC functions can be augmented to attenuate restenosis and atherosclerosis, leading to development of novel therapeutics. 2) Netrin-1 inhibits monocyte activation in a UNC5B (repellant class of netrin-1 receptor)-dependent fashion; and that UNC5B is innovatively regulated by a p47phox-dependent mechanism. Therefore, inhibition of p47phox may potentiate the beneficial effects of netrin-1 in limiting restenosis and atherosclerosis via attenuation of UBC5B expression and UNC5B-dependent monocyte activation. Netrin-1 also inhibits VSMC migration and proliferation via a NO/cGMP/PKG/p38MAPK-dependent mechanism. 3) Administration with netrin-1 or netrin-1 preconditioned EPCs attenuates atherosclerosis in high-fat fed apoE null and LDLR deficient mice. These protective effects are at least in part attributed to augmented EPC function and abrogated monocyte activation, as well as attenuated VSMC proliferation and migration. 4) Endogenous netrin-1 signaling is physiologically protective against restenosis and atherosclerosis, loss of which exaggerates vascular pathologies. We hypothesize that femoral artery injury/high-fat feeding into the netrin-1 or netrin-1/apoE double knockout mice will result in exaggerated restenosis/atherosclerosis. The overall hypothesis is that administration of netrin-1 and netrin-1 preconditioned EPCs remarkably attenuate restenosis and atherosclerosis via mechanisms of augmented EPC function (increased survival, proliferation and homing) to lead to rapid re-endothelialization, attenuated monocyte and VSMC activation, as well as diminished dyslipidemia. Endogenous netrin-1 signaling is physiologically vascular protective, amplification of which with exogenous administration of netrin-1 is necessary to result in sufficient protection, whereas deficiency in the endogenous signaling of netrin-1 (i.e. due to genetic defects) is prone to deteriorated vascular pathologies. Four specific aims are designed to fully address these hypotheses, and accomplishments of the aims may establish netrin-1, netrin-1 pre-conditioned EPCs, and modulators of related pathways as novel therapeutic options for vascular pathologies of restenosis and atherosclerosis.